At 3GPP (Third Generation Partnership Project) RAN (Radio Access Network) #54 plenary meeting a work item (WI) on MIMO with 64QAM (Quadrature Amplitude Modulation) for HSUPA (High Speed Uplink Packet Access) was initiated (see [1]). The WI initialization was a result of extensive studies regarding potential benefits and solutions performed during the study item (SI) phase; see [2] for a summary of the findings.
For a UE (User Equipment) configured in uplink MIMO mode either single or dual-stream transmissions can take place; also referred to as rank 1 and rank 2 transmissions, respectively. Dual-stream transmissions are mainly useful in environments with high SINRs (Signal to Interference plus Noise Ratio), and where the channel exhibits scattering (and/or cross-polarized antennas are used). When single-stream transmissions are scheduled, the pre-coding gain will instead improve the link budget.
Current proposals and discussions for how to design the UL (uplink) MIMO with 64QAM feature can be found in e.g. [3] and the references therein. Some potential design choices for HSUPA MIMO with 64QAM that may be used include:                A pre-coded channel layout where all physical channels are pre-coded with a primary or secondary pre-coding vector is adopted.        P-DPCCH (Primary Dedicated Physical Control Channel), E-DPCCH (E-DCH (Enhanced Dedicated Channel) Dedicated Physical Control Channel), S-E-DPCCH, (Secondary E-DCH Dedicated Physical Data Channel) E-DPDCH (E-DCH Dedicated Physical Data Channel) and HS-DPCCH (High Speed Dedicated Physical Control Channel) are precoded using the primary pre-coding vector.        S-DPCCH (Secondary Dedicated Physical Control Channel) and S-E-DPDCH (Secondary E-DPDCH) are pre-coded using the secondary pre-coding vector.        A common grant which is divided evenly between streams is adopted. Hence, the same transmit power is allocated to E-DPDCH and S-E-DPDCH.        One ILPC (Inner Loop Power Control) operating on the P-DPCCH and one OLPC (Outer loop power control) targeting the quality of the primary data stream E-DPDCH; and/or        The primary data stream E-DPDCH and the secondary data stream S-E-DPDCH use the same channelization code setting (2×SF2 (Spreading Factor 2)+2×SF4 (Spreading Factor 4)) during rank 2 transmissions.        
The approaches described in this section could be pursued, but are not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, the approaches described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.